JUN 15, 2016

Buying an air conditioner is a big decision. It’s the most complex piece of machinery in any home and the most expensive appliance. The customers who are most likely to end up happy with their purchase are those who are well informed about what they want, and what will work in their home.

Here at Donley Service Center, we’ve installed air conditioning units for customers all over the Valley. We’ve decided to help you make the process a little easier by compiling all the information you’ll need to purchase an air conditioner you’ll be happy with for years to come.

What Size Air Conditioner Do You Need?

For this article, we will only focus on whole-home central air conditioning units, not portable or window units. Central air conditioners are mounted either on the roof of a home or outside on the ground. For an air conditioning unit to work most effectively, it must be the right size for your home.

There are several factors that go into determining the right size for any home, including climate. For instance, here in the Phoenix area, a 1.5 ton unit will not adequately cool an area of 900 square-feet, but could cool 1,100 square feet if your home was in Minnesota or Maine. Of course, that is a direct result of the extreme heat here in the Phoenix area. Air conditioners have to work harder to keep a home cool.

Homes will usually need an air conditioner between 3 and 5 tons, depending on the size of your home. Here’s a rough calculation below.

  • 3 tons = 1,500 – 1,800 square feet
  • 3.5 tons = 1,800 – 2,100 square feet
  • 4 tons = 2,100 – 2,400 square feet
  • 5 tons = 2,400 – 3,000 square feet

While the size of your home is an important part of calculating the tonnage of the air conditioner you will need, it’s not the only indicator. The quality of your insulation, doors, windows and ductwork will play a role. An older, less efficient home may need a larger unit to compensate for the more rapid loss of cool air.

What’s the Impact of Buying the Wrong Size?

Buying an air conditioning unit that is a little larger than recommended may seem like a good idea, just to get that extra bit of cooling power, but it’s actually counterproductive. Today more than ever, buying the right size is crucial to keeping a cool, comfortable home without going into shock every time you open the power bill.

Let’s go into a little more detail about the impacts of buying the wrong size air conditioning unit.

Air conditioner is too big: An AC that’s too big will most definitely cool your house quickly, a little too quickly in fact. The unit will shut off before it runs through the complete cycle it was designed for. The heat will seep back into your home, causing the unit to snap back on for another short cycle. The end result is a unit that cycles on and off too frequently and uses more energy than necessary.

Too small: An air conditioner that’s too small may still be able to keep your home cool, but it’s going to work a lot harder to do it. You’ll notice the air conditioner seems to cycle on and run almost constantly. That’s because the AC is playing a constant game of catch-up, trying to cool too large of an area while staying ahead of the heat. This almost constant running will use more energy and shorten the lifespan of the air conditioner.

The right size: A properly sized air conditioning unit will run exactly as it is designed. That means it will run through full cycles and keep your home comfortable, without cycling on too frequently. You’ll be more comfortable without having to watch you electric bill go through the roof.

Efficiency and SEER Rating

Modern air conditioners are designed to use less electricity to cool your home. When it comes to central air conditioning units, the efficiency is measured in terms of the SEER Rating. SEER stands for Seasonal Energy Efficiency Rating and is based on strict, measurable requirements that are regulated by the federal government.

To put it simply, the higher the SEER, the more efficient the unit will be. In many cases, higher SEER rankings will also mean a higher price tag, so finding a happy medium between upfront cost and efficiency is a primary concern for many homeowners.

Today, manufacturers are not allowed to produce units with a rating lower than 14 SEER. There are units available at up to 23 SEER.

Here at Donley Service Center, we find that 16 SEER air conditioners strike a nice balance of efficiency and the upfront cost of the unit. An air conditioner with a 16 SEER rating will be noticeably more efficient than the minimum 14 SEER and will have a more reasonable price tag than an 18 or 20.

You’ve Got an Idea About SEER and Size. What’s Next?

Once you have a good idea about what size air conditioner you might need along with your preferred SEER rating, you can start looking at which brands might appeal to you and how much those units are going for. We know that buying a new air conditioner is a major investment and always work with our customers to keep projects on budget.

Consult with a reputable contractor who can do a thorough inspection of your home and verify your sizing needs. It may end up that you need a unit that’s a little larger or smaller than anticipated. Your technician may also find small issues that could be addressed before installation, such as leaks in ductwork or areas that could use more insulation.


The most important aspect when it comes to installation is choosing an HVAC contractor you can trust to perform the work. That means a company that is licensed, bonded and has a reputation for quality work and customer satisfaction.

At Donley Service Center, we’ve been installing air conditioning units in the Phoenix area for 40 years. We stand behind the quality of our work 100 percent.

It’s important to note that purchasing the unit itself through the company that will perform the installation will save you money and provide peace of mind. At Donley, we offer the best warranty in the business on our installations in addition to the manufacturer’s warranty.

After Installation: Optimizing Your Performance

Once you have the perfect size air conditioner installed in your home, a few simple additions will help ensure your unit runs at its peak efficiency and performance for years to come.

Thermostat: A programmable thermostat will allow you to fine-tune the cooling schedule so you don’t waste energy. You can take the savings a step further by investing in a smart thermostat such as Nest. These thermostats will automatically learn your daily routines, such as when you leave for work and when you come home, and adjust automatically to maximize efficiency.

Air Filter: Change your air filter every month, even if the manufacturer recommends changing it less frequently. There’s a lot of dust here in the Phoenix area and the best way to keep those particulates out of your air conditioning system is to change the filter regularly.

We also recommend against the use of spun fiberglass filters. While they only cost a dollar or two, these filters will only filter out large dust particles, allowing plenty of pollutants to get through. The best option for disposable filters is a pleated variety. These will do a much better job of capturing the finer particles and keep them out of your air conditioner.

Another option would be electrostatic air filters. These are made to last a lifetime and work just as effectively as the pleated variety. However, you’ll have to clean the filter out yourself every 30 days. If you don’t have that kind of self-discipline, this isn’t the filter for you.

Maintenance: You’ll also get a much longer lifespan out of your new air conditioner with periodic maintenance. It simply involves having a technician come out once a season to make sure everything is running properly. The technician will perform a full diagnostic and make any small adjustments that might be needed, including a top-off of the Freon if it’s needed. Taking care of an air conditioner is kind of like caring for your car; with a little attention to regular maintenance, it will be reliable and efficient.

Still Have Questions? Contact Donley Service Center Directly

If you still have questions about buying a new air conditioner for your home, feel free to speak with one of our experts directly. We can help you choose a reliable and efficient air conditioner that’s guaranteed to keep your home cool.

Call 602-899-1564. Our experienced technicians can help take the mystery out of sizing an air conditioner or choosing the right model. Our customers have counted on Donley to provide trustworthy, quality service for four decades.